Doctor put right on a fool (5)
I believe the answer is:
moron
'a fool' is the definition.
(I've seen this in another clue)
'doctor put right on' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'put right' becomes 'r' (I've seen this in other clues).
'mo'+'r'+'on'='MORON'
(Other definitions for moron that I've seen before include "Clot" , "Idiot" , "Blockhead" , "Foolish or stupid person" , "Person of subnormal intelligence" .)